1. Field of the Invention
The present invention relates to a navigation apparatus. More particularly, it relates to a technology for, when a vehicle equipped with the navigation apparatus has traveled an unregistered road about which road data is not registered in the navigation apparatus, creating road data about the unregistered road from the traveling path of the vehicle.
2. Description of Related Art
Conventionally, a navigation apparatus which creates road data about an unregistered road and registers the road data in road map data when a vehicle equipped with the navigation apparatus has traveled the unregistered road about which road data is not registered in the road map data is known. For example, patent reference 1 discloses a navigation apparatus which stores the traveling path of a vehicle when the vehicle has traveled an off-road, and, after that, reads the traveling path so as to display it, and a navigation method at a time when the vehicle is traveling an off-road. This navigation apparatus disclosed by patent reference 1 creates road data automatically on the basis of the traveling path of the vehicle in a section in which the current position of the vehicle cannot be map-matched onto any road indicated by road data. If the navigation apparatus can determine that the current position of the vehicle is out of any road indicated by road data when the vehicle has traveled from a registered road indicated by road data created automatically to an unregistered road about which road data is not registered, the navigation apparatus defines, as a branch point of the registered road, the current position of the vehicle, and creates road data automatically on the basis of the traveling path of the vehicle after the branch point.
Patent reference 2 discloses a method of creating road map data which is applied in order to create road map data for use in a navigation system or the like. In accordance with this road-map-data creation method, the traveling path M of a vehicle which has traveled an unknown route extending from a first point A (i.e., a vehicle departure point) whose position on the road map data is known to a second point B (i.e., a vehicle return point) whose position on the road map data is known, the first and second points being set up manually by the user, is obtained, a rotation operation around the first point A and a scaling operation are performed on the traveling path M of the vehicle in order to make the end point of the traveling path M agree with the second point B so that the traveling path M of the vehicle is corrected for, and road map data is created on the basis of the corrected traveling path. According to this creation method of creating road map data, only one drive of the vehicle along a route about which road map data should be created makes it possible to easily create correct road map data about a road, such as a road newly constructed, without having to wait for supply of road map data obtained by taking an aerial photograph or the like of the road.
[Patent reference 1] JP-A 2002-357431
[Patent reference 2] JP-A 06-201392
However, the prior art navigation apparatus disclosed by patent reference 1 has the following problems. That is, because the prior art navigation apparatus is so designed as to carry out a map matching process of comparing road data with the current position of the vehicle on the assumption that the vehicle travels a road, it is difficult for the prior art navigation apparatus to determine that the current position of the vehicle is out of any registered road indicated by the road data when it is placed in a matching state in which the current position of the vehicle is map-matched onto a registered road, and, when the vehicle travels an unregistered road while the prior art navigation apparatus is placed in a free state (i.e., a state which is not the matching state), the prior art navigation apparatus may determine that the current position of the vehicle is on a registered road incorrectly if the registered road runs in parallel with and in the vicinity of the traveling path of the vehicle. On the other hand, when there are two or more roads near the current position of the vehicle, the prior art navigation apparatus does not determine that the current position of the vehicle is on a registered road until it will have continued to recognize a similarity in the shape of the traveling path of the vehicle and consistency of the current position of the vehicle with the registered road while the vehicle has been traveling a predetermined distance or longer. A problem with the prior art navigation apparatus is therefore that when it detects the coordinates of an unregistered road and registered roads to which the unregistered road is connected from the traveling path of the vehicle in a section where the prior art navigation apparatus is placed in the free state in which the current position of the vehicle is out of any registered road, large errors occurs in the detection results.
A problem with the prior art creation method of creating road map data disclosed by patent reference 2 is that a navigation system using the creation method cannot detect any unregistered road when the user cannot operate the navigation system even if the user wants to operate it (e.g., when the user is driving a well-trafficked road) or when the user has forgotten to operate the navigation system, the navigation system cannot detect any unregistered road, and, when the user has failed to operate it (when the user is driving an unfamiliar area, the user may not perform operations correctly to set up the first and second points), the navigation system specifies roads connected to an unregistered road incorrectly.